applied sciences Article
Effects of Titanate Coupling Agent on Engineering Properties of Asphalt Binders and Mixtures Incorporating LLDPE-CaCO3 Pellet Mohd Rosli Mohd Hasan 1, *, Zhanping You 2, * ID , Mohd Khairul Idham Mohd Satar 3 , Muhammad Naqiuddin Mohd Warid 3 , Nurul Hidayah Mohd Kamaruddin 4 , Dongdong Ge 2 and Ran Zhang 5 1 2 3 4 5
*
School of Civil Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang, Malaysia Department of Civil and Environmental Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA;
[email protected] Department of Geotechnics and Transportation, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia;
[email protected] (M.K.I.M.S.);
[email protected] (M.N.M.W.) Faculty of Civil and Environmental Engineering, Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja, Johor, Malaysia;
[email protected] School of Highway, Chang’an University, South Erhuan Middle Section, Xi’an 710064, Shaanxi, China;
[email protected] Correspondence:
[email protected] (M.R.M.H.);
[email protected] (Z.Y.); Tel.: +60-604-599-6288 (M.R.M.H.); +1-906-487-1059 (Z.Y.)
Received: 31 May 2018; Accepted: 21 June 2018; Published: 24 June 2018
Abstract: This study was initiated to evaluate the performance of asphalt binders and mixtures incorporating linear low-density polyethylene- calcium carbonate (LLDPE-CaCO3 ) pellet, either with or without titanate coupling agent. The detailed manufacturing process of modifier pellets was displayed. The coupling agent was used to enhance the cross-linking between materials by means of winding up covalent bonds or molecule chains, thus improving the performance of composites. In the preparation of modified bitumen, the preheated asphalt binder was mixed with the modifiers using a high shear mixer at 5000 rpm rotational speed for 45 min. Experimental works were conducted to evaluate the performance of asphalt binders in terms of volatile loss, viscosity, rutting potential, and low temperature cracking. Meanwhile, the asphalt mixtures were tested using the flow number test and tensile strength ratio (TSR) test. The addition of LLDPE-CaCO3 modifiers and coupling agent does not significantly affect the volatile loss of modified asphalt binders. The addition of modifiers and coupling agent has significantly improved the resistance to permanent deformation of asphalt binders. Even though, the addition of LLDPE-CaCO3 modifier and coupling agent remarkably increased the mixture stiffness that contributed to lower rutting potential, the resistance to low temperature cracking of asphalt binder was not adversely affected. The combination of 1% coupling agent with 3% PECC is optimum dosage for asphalt binder to have satisfactory performance in resistance to moisture damage and rutting. Keywords: asphalt modification; coupling agent; rheological behavior; plastic; calcium carbonate powder
1. Introduction Over decades, a wide range of modification at macro, meso-, micro- and nano-scales have been conducted to improve the performance of asphalt pavement [1]. This is essential to design durable, Appl. Sci. 2018, 8, 1029; doi:10.3390/app8071029
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safe and efficient asphalt pavement that can function efficiently across a wide range of temperatures and distresses. Polymer modified binders have got increasing use on improving the resistance to thermal cracking and permanent deformation, as well as reducing the fatigue cracking potential of asphalt pavement [2,3]. Brown et al. [4] mentioned that an ideal asphalt condition should exhibit both: (a) Relatively high stiffness at high temperature to prevent rutting and shoving and; (b) great adhesion between asphalt binder and aggregates matrices in the presence of water to reduce moisture induced damage, for example stripping. Additionally, Chen et al. [5] mentioned that the asphalt is continuously exposed to a wide range of climates, loading rate and time, but it does not have essential engineering properties to sustain those situations, where the binder is soft under hot summer days and brittle in the freezing condition. Various types of polymer have been used to chemically or mechanically improve the properties of asphalt binder, which can be classified into three different categories: elastomer, plastomer and reactive polymers [4,6,7]. The application of polymers in the asphalt pavement has been growing rapidly since the early 1970s. Based on previous studies, modifications of asphalt binder using polymer materials can significantly improve the properties of asphalt material, such as reducing the temperature susceptibility, providing better rheological characteristics, as well as enhancing the material durability [3,8,9]. Polyethylene (PE) and polyethylene-based copolymers (new or recycled) has been used to modify the performance of asphalt binder and mixture over many years [2,10]. The PE and polypropylene (PP) are categorized as plastomers which can bring a high rigidity to the material and improve the resistance to permanent deformation under traffic load [11,12]. A study was performed by Habib et al. [13] to evaluate the rheological properties and interaction of asphalt binder with different thermoplastics, such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and PP. Based on their study, the viscoelastic behavior of asphalt binder was significantly affected by the modifier concentration, bitumen grade and the temperature. In addition, based on the overall studies, the best results occurred when the polymer concentration was limited to 3%, which resulted from the thermodynamically stable structure condition. This had significantly improved the resistance to rutting, fatigue, and temperature susceptibility. Limestone (CaCO3 ) is an inert material which has been used as an additive in asphalt mixture for more than 100 years. However, the hydrated lime came into regular use only just in the 1980s. Several states including Georgia, Nevada, Texas, Virginia, and Utah used lime to solve the water susceptibility issue on asphalt pavement [14]. CaCO3 is the most widely used filler in thermoplastics because of its low cost and superior mechanical properties. Much effort has been focused to increase mechanical properties such as tensile and flexural strength, impact resistance of CaCO3 -filled PP, HDPE, LDPE, and LLDPE composites [15]. The term “lime” is used referring to either quicklime or hydrated lime which comes originally from limestone. Calcinations process of limestone dissociated the calcium from carbon dioxide, leaving calcium oxide. This is known as quicklime, it is then combined with water to form hydrated lime. In the asphalt industry, the lime generally refers to hydrated lime or calcium hydroxide [16]. The fineness and high surface area of hydrated lime contributes to a high speed of chemical reaction. Hydrated lime is the only form of lime which has been shown to be useful in controlling stripping. Many aggregates are quite acidic and the asphalt binder also contains acids, the ions present at the interface of both materials repelled each other electrically. The presence of lime could neutralize the acidic aggregates and asphalt binder, which provide opposite-charge ions to enhance adhesion [16]. Thus, lime in asphalt mixture is not only used as an anti-stripping agent, but it may improve mixture stiffness, reduce plasticity index when clays are present and reduce the oxidation rate [14,16]. Lu and Isacsson [17] revealed that, even though the thermoplastic modifiers had improved the viscosity and stiffness of asphalt binder, it did not significantly help in terms of elastic behavior. The embrittlement makes asphalt susceptible to fracture, especially when subjected to high levels of stress [18]. The polymer should be homogeneously dispersed into asphalt to ensure proper adhesion of the asphalt binder. However, incompatibility between the binder and the polymer is sometimes
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inevitable. As a result, it is difficult to establish the bond, either in terms of a physical or chemical manner [18,19]. Prior to gaining a better performance, an application of coupling agent in organic materials or treating inorganic fillers has been used. This enhances the materials cross-linking by means of winding up covalent bonds or molecule chains, thus improving the performance of composites [20,21]. It was found that a small amount of coupling agent could increase shear resistance in mechanical properties [20]. There are various types of coupling agents that have been used to improve the bonding of composite materials such as: Silane, zirconate, dicarboxylic anhydry-dem, titanate and phosphate ester. However, the most important commercial coupling agents are formed by silane and titanate [22]. A titanate coupling agent has been used in enhancing the bonding in CaCO3 –thermoplastic composites [23]. A study conducted by Atikler et al. [15] showed that a silane coupling agent had significantly ameliorated the mechanical properties of the HDPE–fly ash composites. Sae-oui et al. [24] reported that excessive use of a silane coupling agent could cause a negative effect on certain properties such as modulus and hardness due to plasticizing effect. Additionally, Chen et al. [25] also concluded that too much of a titanate coupling agent resulted in polymer bridging, and reduced the phase boundary condition. It would also influence the economic aspect, whereby the excess of a coupling agent could increase the cost of production. Former studies [26–28] had recommended using the titanate-coupling agent in a range of 0.1 wt % to 0.5 wt % to attain the best performance based on the adhesion test. Even though various types of polymers have been used to enhance the performance of asphalt composite, only a few of them are considered as satisfactory based on the performance and economic standpoints [29,30]. In this study, newly manufactured asphalt modifiers that comprised of LLDPE and CaCO3 with or without titanate coupling agent was used to enhance the engineering properties of asphalt binder and asphalt mixture durability towards various distresses. 2. Materials and Methods 2.1. Materials 2.1.1. Asphalt Binder and Aggregate The basic materials that used in this study were obtained from a local source in Hancock, Michigan. The PG 58-28 was used as a control binder. The aggregate gradation used was based on Michigan Department of Transportation (MDOT) specifications for Upper Peninsula region. The nominal maximum aggregate size of the gradation is 9.5 mm and the designed traffic level is less than three million equivalent single axles loads (ESALs) based on the Superpave asphalt mixture design procedure. 2.1.2. Coupling Agent For this project the coupling agent Ken-React® CAPS® L® 12/L was used [31]. Ken-React® CAPS® L® 12/L is a neoalkoxy titanate, with a specific gravity of 0.95, and is in the form of an off-white/beige solid pellet. Ken-React® CAPS® L® 12/L was used as-received. Figure 1 shows the chemical structure of the Ken-React® LICA® 12 (20% Active Portion of CAPS® L® 12/L). The chemical name for Ken-React® CAPS® L® 12/L is titanium IV 2,2 (bis-2-propenolatomethyl) butanolato, tris(dioctyl) phosphate-O [32]. Figure 2 shows the appearance of coupling agent.
For this project the coupling agent Ken‐React CAPS L 12/L was used [31]. Ken‐React CAPS L® 12/L is a neoalkoxy titanate, with a specific gravity of 0.95, and is in the form of an off‐white/beige solid pellet. Ken‐React® CAPS® L® 12/L was used as‐received. Figure 1 shows the chemical structure of the Ken‐React® LICA® 12 (20% Active Portion of CAPS® L® 12/L). The chemical name for Ken‐ React® CAPS® L® 12/L is titanium IV 2,2 (bis‐2‐propenolatomethyl) butanolato, tris(dioctyl) Appl. Sci. 2018, 8, 1029 4 of 15 phosphate‐O [32]. Figure 2 shows the appearance of coupling agent.
Figure 1. Chemical structure of Ken-React® LICA® 12 (20% active portion of CAPS® L® 12/L).
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Figure 1. Chemical structure of Ken‐React® LICA® 12 (20% active portion of CAPS® L® 12/L).
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Figure 2. Titanate coupling agent (shown in red circle) mixed with LLDPE pellets. Figure 2. Titanate coupling agent (shown in red circle) mixed with LLDPE pellets.
2.1.3. Manufacturing Process of Modifier Pellets 2.1.3. Manufacturing Process of Modifier Pellets A V‐cone mixer was used operating at 24 rpm for four minutes to mix the Ken‐React® CAPS® L® A V-cone mixer was used operating at 24 rpm for four minutes to mix the Ken-React® CAPS® 12/L and LLDPE pellets. The modifier pellets were prepared using extrusion equipment in the L® 12/L and LLDPE pellets. The modifier pellets were prepared using extrusion equipment in the Chemical Engineering Department at Michigan Technological University. An American Leistritz Chemical Engineering Department at Michigan Technological University. An American Leistritz Extruder Corporation, model ZSE 27 has a 27 mm co‐rotating intermeshing twin‐screw extruder with Extruder Corporation, model ZSE 27 has a 27 mm co-rotating intermeshing twin-screw extruder with ten heating zones, a length/diameter ratio of 40 and two stuffers was used to produce the modifier ten heating zones, a length/diameter ratio of 40 and two stuffers was used to produce the modifier pellets. Two Schenck AccuRate gravimetric feeders were used to accurately control the amount of pellets. Two Schenck AccuRate gravimetric feeders were used to accurately control the amount of LLDPE, CaCO3 and the coupling agent supplied into the extruder. Figure 3 illustrates the screw LLDPE, CaCO3 and the coupling agent supplied into the extruder. Figure 3 illustrates the screw design® design that used during manufacturing of pellet modifiers [33]. The LLDPE and LLDPE/Ken‐React that used during manufacturing of pellet modifiers [33]. The LLDPE and LLDPE/Ken-React® CAPS® ® ® CAPS L 12/L coupling agent was added to zone 1. Meanwhile, CaCO3 was added in Zone 5. L® 12/L coupling agent was added to zone 1. Meanwhile, CaCO3 was added in Zone 5. After passing through the extruder, the polymer strands (3 mm in diameter) enter a 3 m long water bath (Sterling Blower model WT-1008-10) and then a pelletizer (Accu-grind Conair Model 304) produced nominally 3 mm diameter by 3 mm long pellets. The final product of the manufacturing process is shown in Figure 4. After compounding, the pelletized composite resin was dried in an indirect heated dehumidifying oven (Bry Air RD-20) at 60 ◦ C for 7 h. It was then stored in sealed moisture barrier bags prior to mixing with asphalt binder [34]. The extrusion conditions for different modifiers are shown in Table 1. Three different formulations were extruded. The first was called PECC, which contained 70 wt % LLDPE and 30 wt % CaCO3 . The second was called PECC-1CA, which contained 69.3 wt % LLDPE, 29.7 wt % CaCO3, and 1 wt % Ken-React® CAPS® L® 12/L coupling agent. The third was called PECC-2CA, which contained 29.4 wt % CaCO3, 68.6 wt % LLDPE, and 2 wt % Ken-React® CAPS® L® 12/L coupling agent.
Figure 3. Extruder screw design.
Chemical Engineering Department at Michigan Technological University. An American Leistritz Extruder Corporation, model ZSE 27 has a 27 mm co‐rotating intermeshing twin‐screw extruder with ten heating zones, a length/diameter ratio of 40 and two stuffers was used to produce the modifier pellets. Two Schenck AccuRate gravimetric feeders were used to accurately control the amount of LLDPE, CaCO3 and the coupling agent supplied into the extruder. Figure 3 illustrates the screw ® design that used during manufacturing of pellet modifiers [33]. The LLDPE and LLDPE/Ken‐React Appl. Sci. 2018, 8, 1029 5 of 15 ® ® CAPS L 12/L coupling agent was added to zone 1. Meanwhile, CaCO3 was added in Zone 5.
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Figure 3. Extruder screw design. Figure 3. Extruder screw design.
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After passing through the extruder, the polymer strands (3 mm in diameter) enter a 3 m long water bath (Sterling Blower model WT‐1008‐10) and then a pelletizer (Accu‐grind Conair Model 304) produced nominally 3 mm diameter by 3 mm long pellets. The final product of the manufacturing process is shown in Figure 4. After compounding, the pelletized composite resin was dried in an indirect heated dehumidifying oven (Bry Air RD‐20) at 60 °C for 7 h. It was then stored in sealed moisture barrier bags prior to mixing with asphalt binder [34].
Figure 4. Final product of manufactured pellets. Figure 4. Final product of manufactured pellets.
The extrusion conditions for different modifiers are shown in Table 1. Three different Table 1. Extrusion conditions. formulations were extruded. The first was called PECC, which contained 70 wt % LLDPE and 30 wt % CaCO3Material . The second was called PECC‐1CA, which contained 69.3 wt % LLDPE, 29.7 wt % CaCO 3, Number PECC PECC-1CA PECC-2CA ® ® ® and 1 wt % Ken‐React CAPS L 12/L coupling agent. The third was called PECC‐2CA, which Extrusion Date March 12 2013 March 12 2013 March 12 2013 contained 29.4 wt % CaCO 3, 68.6 wt % LLDPE, and 2 wt % Ken‐React® CAPS® L® 12/L coupling agent. Extruder, rpm 250 250 250 Motor Amperage, % 27 27 27 Table 1. Extrusion conditions. Melt Temperature, ◦ C 244 244 244 Melt Pressure, psig 80 80 80 PECC‐1CA PECC‐2CA 6.0 Material Number #2 Feeder Setting, lb/h 6.0 PECC 6.0 Extrusion Date March 12 2013 March 12 2013 March 12 2013 CaCO Material in Feeder #2 CaCO CaCO3 3 3 Extruder, rpm 250 250 250 #3 Feeder Setting, lb/h 14 14 14 Motor Amperage, % 27 27 Material in Feeder #3 LLDPE 27 LLDPE + CAPS LLDPE + CAPS Melt Temperature, °C 244 244 244 Vacuum Port 1 atm 1 atm 1 atm Melt Pressure, psig 80 80 80 Zone 5 Side Stuffer Setting, rpm 300 300 300 #2 Feeder Setting, lb/h 6.0 6.0 6.0 Feeder at Zone 5 CaCO3 CaCO3 CaCO3 CaCO3 CaCO3 Material in Feeder #2 CaCO3 Zone 7 Side Stuffer setting, rpm 300 300 300 #3 Feeder Setting, lb/h 14 14 14 Feeder at Zone 7 none none none Material in Feeder #3 LLDPE LLDPE + CAPS LLDPE + CAPS Feed Section Temperature H2 O Cooled H2 O Cooled H2 O Cooled Vacuum Port 1 atm 1 atm 1 atm ◦ Zone 1 Temperature, C 175 175 175 Zone 5 Side Stuffer Setting, rpm 300 300 300 Zone 2 Temperature, ◦ C 195 195 195 CaCO3 CaCO3 Feeder at Zone 5 CaCO3 Zone 3 Temperature, ◦ C 210 210 210 Zone 7 Side Stuffer setting, rpm Feeder at Zone 7 Feed Section Temperature Zone 1 Temperature, °C Zone 2 Temperature, °C Zone 3 Temperature, °C Zone 4 Temperature, °C Zone 5 Temperature, °C Zone 6 Temperature, °C
300 none H2O Cooled 175 195 210 220 220 220
300 none H2O Cooled 175 195 210 215 220 220
300 none H2O Cooled 175 195 210 215 215 215
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Table 1. Cont. Material Number ◦C
Zone 4 Temperature, Zone 5 Temperature, ◦ C Zone 6 Temperature, ◦ C Zone 7 Temperature, ◦ C Zone 8 Temperature, ◦ C Zone 9 Temperature, ◦ C Zone 10 Temperature, ◦ C Die Type and Gap Pelletizer Setting at 8/Bath Output Rate, lbs/h
PECC
PECC-1CA
PECC-2CA
220 220 220 220 220 220 220 3 × 3 mm H2 O bath 20
215 220 220 220 220 220 220 3 × 3 mm H2 O bath 20
215 215 215 215 215 215 220 3 × 3 mm H2 O bath 20
Notes: (1) LLDPE and Ken-React® CAPS® L® 12/L mixed in V cone blender for 4 min at 24 rpm in 2 lb batches and then placed in Feeder 3. (2) Approximately 20 lbs of each extruded material was produced. (3) Feeder 3 helix: 0.5” open helix with end stub and 0.75” nozzle side discharge. (4) Feeder 3 Toshiba laptop feeder3_VectraA950RX0.5inopen0.75insidedischargejak.par. (5) Feeder 2 helix: 0.75” open helix with 0.75” ID polyliner. (6) Feeder 2 NEC laptop Thermocarb file. (7) Extruder screw 5-14-05 design used from American Leistritz. Extruder screw cleaned in sand bath prior to use. (8) Purged with LLDPE at end of extrusion run to clean out extruder.
2.2. Methods 2.2.1. Preparation of Modified Asphalt Binder The modified asphalt binders were prepared using a high shear mixer. The binder and modifiers were properly mixed to ensure the materials were evenly dispersed in asphalt binder. The temperature that used for the production of modified asphalt binder is at 170 ◦ C. In the asphalt binder preparation process, about 500 g of asphalt binder PG 58-28 was poured into a one liter metal container. Then, an adequate amount of modifier was added to the same container and heated up in an oven for about two hours prior to the mixing process. After two hours of inducing the melting process, the binder and modifier were stirred using a high shear mixer at 5000 rpm rotational speed for 45 min. Based on literature review, LLDPE-related modifiers were used as asphalt modifiers in a range of 2% to 6% based on the weight of asphalt binder [11,13,35–38]. Based on the range, the amounts of modifier incorporated in the asphalt binder were decided at 3% and 5% based on the asphalt binder weight. At least three replicate specimens were used for all the asphalt binder and asphalt mixture tests. 2.2.2. Preparations of Asphalt Mixture Specimen A bucket mixer was used to blend the aggregates and asphalt binder. The sample was compacted using a gyratory compactor at 86 gyrations. Prior to compaction, the mixture was heated in an oven for two hours to simulate the short-term aging condition that occurs during preparation of asphalt mixture in the field. The Superpave specifications [39–41] were referred during the preparation of asphalt mixture. 2.2.3. Asphalt Binder Test Method The rolling thin film oven (RTFO) was used to quantify the volatiles lost (mass loss) during the short-term aging process of asphalt binder. Based on the Superpave Specification, the mass loss of asphalt binder should be less than 1 wt % to ensure the asphalt binder not to lose a significant number of volatiles over its life. The rotational viscometer was used to determine the viscosity of asphalt binders at high temperature. During the sample preparation, about 10.5 g asphalt binder is required for each sample, and spindle #27 was used in this test. This test measures the required torque value to maintain a constant rotational speed (20 rpm) of a cylindrical spindle under a constant temperature. The results were recorded in centipoises (cP) at one-minute intervals for a total of three readings.
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In this study, the multiple stress creep recovery (MSCR) was conducted by introducing the RTFO aged asphalt binder specimen to the repeated creep and recovery process at high temperature. The test has been conducted in accordance with AASHTO TP 70-13 at 58 ◦ C, which is the high temperature grade of selected asphalt binder, PG 58-28. The 25 mm diameter with 1 mm thickness circular disk-shaped asphalt binder sample was used. Two stress levels were introduced to the sample, which were 0.1 kPa and 3.2 kPa at one second loading time and nine seconds recovery time while performing the test [42,43]. The test started with 0.1 kPa stress for ten cycles without time lags, and proceeded with 3.2 kPa stress under the same number of cycles. The new MSCR test, which is conducted based on AASHTO T 350-14, conducted 20 cycles 0.1 kPa stress loading and unloading. The MSCR test result may be different if conducted in accordance with AASHTON T 350 [44,45]. The bending beam rheometer (BBR) test was performed in accordance with AASHTO T 313; a simply supported beam of asphalt binder was subjected to a constant load of 980 mN for four minutes. The test was conducted at −12 ◦ C, −18 ◦ C and −24 ◦ C to define the critical cracking temperature of control and modified binders. 2.2.4. Asphalt Mixture Test Method The flow number test was referred to a dynamic creep or repeated load testing. Basically, a 0.1 s loading followed by a 0.9 s dwell (rest time) was applied to the specimen. Additionally, an effective temperature of 45 ◦ C, often referred to as rutting temperature was used in this test [46,47]. Prior to the testing, the specimens were conditioned at 45 ◦ C. Appl. Sci. 2018, 8, x FOR PEER REVIEW 7 of 15 The tensile strength ratio (TSR) was used to evaluate the moisture susceptibility of asphalt temperature of 45 °C, often referred to as rutting temperature was used in this test [46,47]. Prior to mixture. The moisture susceptibility was evaluated by comparing the indirect tensile strength (ITS) the testing, the specimens were conditioned at 45 °C. of asphalt mixtures in dry and wet conditions. The ITS test was performed according to AASHTO The tensile strength ratio (TSR) was used to evaluate the moisture susceptibility of asphalt T283. The specimens were tested at the room temperature and constant loading speed, 0.085 mm/s. mixture. The moisture susceptibility was evaluated by comparing the indirect tensile strength (ITS) The specimen of asphalt mixtures in dry and wet conditions. The ITS test was performed according to AASHTO was subjected to compression loads which act parallel to the vertical diameter plane. T283. The specimens were tested at the room temperature and constant loading speed, 0.085 mm/s.
3. Characterization of Asphalt Binder The specimen was subjected to compression loads which act parallel to the vertical diameter plane. 3. Characterization of Asphalt Binder 3.1. Volatile Loss 3.1. Volatile Loss At elevated temperature, the smaller molecules from asphalt binder are driven off, resulting in an increase of the At elevated temperature, the smaller molecules from asphalt binder are driven off, resulting in asphalt’s viscosity. The effects of heat and flowing air on a thin film of semi-solid an increase of the asphalt’s viscosity. The effects of heat and flowing air on a thin film of semi‐solid asphaltic material are considered in this procedure. Figure 5 presents the mean mass loss values of each specimenasphaltic material are considered in this procedure. Figure 5 presents the mean mass loss values of tested using short-term aging protocol. Based on the test results, incorporation of each specimen tested using short‐term aging protocol. Based on the test results, incorporation of modifiers andmodifiers and coupling agent do not significantly affect the volatile loss of modified asphalt binders coupling agent do not significantly affect the volatile loss of modified asphalt binders compared to control binder PG 58-28. compared to control binder PG 58‐28.
Mean Mass loss (%)
0.12 0.1 0.08 0.06 0.04 0.02 0
Figure 5. Figure 5. Mass loss test results of each asphalt binder. Mass loss test results of each asphalt binder. 3.2. Rotational Viscosity Figures 6 and 7 show the results of asphalt binders modified using PECC and PECC‐CA modifiers. Modified asphalt binders have higher viscosity value compared to the control asphalt binder. The addition of a titanate coupling agent has slightly increased the viscosity and consistency of asphalt binders, except for the specimen prepared using 3% PECC‐1CA. The increaments are ranging from 4% to 40% depending on the percentage of coupling agent and test temperature.
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3.2. Rotational Viscosity Figures 6 and 7 show the results of asphalt binders modified using PECC and PECC-CA modifiers. Modified asphalt binders have higher viscosity value compared to the control asphalt binder. The addition of a titanate coupling agent has slightly increased the viscosity and consistency of asphalt binders, except for the specimen prepared using 3% PECC-1CA. The increaments are ranging from 4% to 40% depending on the percentage of coupling agent and test temperature. Hypothetically, the viscosity of asphalt binder could also be used as an early indicator of resistance to permanent deformation. Whereas, higher viscosity could sustain higher temperature before the binder flow or change its physical behavior. In the field, the melting temperature can be related to the atmospheric ambient temperature. In this study, the addition of modifiers and coupling agent has significantly improved the resistance to permanent deformation of asphalt binders. Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 15 Appl. Sci. 2018, 8, x FOR PEER REVIEW
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.s).s) Viscosity (Pa Viscosity (Pa
1 1
B B A A
0.1 0.1
0.01 0.01130 130
A : Ideal Viscosity Range for Mixing A :: Ideal Ideal Viscosity Viscosity Range Range for for Compaction Mixing B B : Ideal Viscosity Range for Compaction
150 170 (°C) 150 Temperature 170 Temperature (°C)
3% PECC-2CA 3% PECC PECC-2CA 3% 3% PECC-1CA PECC 3% 3% 58-28 PECC-1CA PG PG 58-28
190 190
Figure 6. Modified Asphalt Binder Viscosity at Low Modifier Percentage. Figure 6. Modified Asphalt Binder Viscosity at Low Modifier Percentage. Figure 6. Modified Asphalt Binder Viscosity at Low Modifier Percentage.
Viscosity (Pa.s) Viscosity (Pa.s)
1 1
0.1 0.1
B AB A
0.01 0.01130 130
5% PECC-2CA 5% PECC-1CA PECC-2CA 5% 5% PECC PECC-1CA 5% 5% 58-28 PECC PG PG 58-28
A : Ideal Viscosity Range for Mixing A :: Ideal Ideal Viscosity Viscosity Range Range for for Compaction Mixing B B : Ideal Viscosity Range for Compaction
150 170 150 Temperature 170 (°C) Temperature (°C)
190 190
Figure 7. Modified asphalt binder viscosity at high modifier percentage. Figure 7. Modified asphalt binder viscosity at high modifier percentage.
Figure 7. Modified asphalt binder viscosity at high modifier percentage. 3.3. Multiple Shear Creep Recovery 3.3. Multiple Shear Creep Recovery 3.3. Multiple Shear Creep Recovery The DSR with G*/sin δ (AASHTO M320) is the typical parameter for rutting prediction of asphalt The DSR with G*/sin δ (AASHTO M320) is the typical parameter for rutting prediction of asphalt pavement. However, this method has been revised to provide a better prediction on the rutting The DSR with G*/sin this δ (AASHTO M320) isMSCR. the typical parameter for rutting prediction of asphalt pavement. However, method binder has been to provide a better prediction on the rutting performance of modified asphalt by revised This method measures the permanent strain performance of modified asphalt binder by MSCR. This method measures the permanent strain pavement. However, this method has been revised to provide a better prediction on the rutting accumulated in the binder after designated cycles of shear loading and unloading. In which, lower accumulated in the binder after designated cycles of shear loading and unloading. In which, lower performance of modified asphalt binder by MSCR. This method measures the permanent strain permanent shear strain indicates higher rutting resistance of the pavement. permanent shear strain indicates higher rutting resistance of the pavement. accumulated in the binder after designated cycles of binder shear loading and unloading. In which, lower Subsequently, the rutting resistance of asphalt is characterized using non‐recoverable Subsequently, the rutting higher resistance of asphalt binder compliance (J nr) which is considered as the best approach to replace the current Superpave testing permanent shear strain indicates rutting resistance of is thecharacterized pavement. using non‐recoverable compliance (Jnr) which is considered as the best approach to replace the current Superpave testing method, G*/sin δ (ω = 10 rad/s) [43,48]. Additionally, the percent recovery (R) is also determined in method, G*/sin δ (ω = 10 rad/s) [43,48]. Additionally, the percent recovery (R) is also determined in order to understand the high temperature viscoelastic deformation properties [43], where higher R order to understand the high temperature viscoelastic deformation properties [43], where higher R value indicates a better resistance to rutting. Meanwhile, a lower J nr value shows a better resistance to value indicates a better resistance to rutting. Meanwhile, a lower Jnr value shows a better resistance to permanent deformation (rutting). permanent deformation (rutting). The mean recovery percentage (n = 3) of the tested asphalt binders are presented in Figures 8 The mean recovery percentage (n = 3) of the tested asphalt binders are presented in Figures 8 and 9. Based on the non‐recoverable compliance criteria, the results show that the modified binders
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Subsequently, the rutting resistance of asphalt binder is characterized using non-recoverable compliance (Jnr ) which is considered as the best approach to replace the current Superpave testing method, G*/sin δ (ω = 10 rad/s) [43,48]. Additionally, the percent recovery (R) is also determined in order to understand the high temperature viscoelastic deformation properties [43], where higher R value indicates a better resistance to rutting. Meanwhile, a lower Jnr value shows a better resistance to permanent deformation (rutting). The mean recovery percentage (n = 3) of the tested asphalt binders are presented in Figures 8 and 9. Appl. Sci. 2018, 8, x FOR PEER REVIEW 9 of 15 9 of 15have BasedAppl. Sci. 2018, 8, x FOR PEER REVIEW on the non-recoverable compliance criteria, the results show that the modified binders lower continuously multiple loading action on the sample. Referring to the specimens prepared using 3% rutting potential as compared to the control binder, PG 58-28. Additions of newly manufactured pelletscontinuously multiple loading action on the sample. Referring to the specimens prepared using 3% have significantly increased the resistance to permanent deformation by at least 27% greater PECC‐1CA and 3% PECC‐2CA, application of 1% coupling agent in the PECC material represents PECC‐1CA and 3% PECC‐2CA, application of 1% coupling agent in the PECC material represents than PG 58-28 binder. Asphalt binder modified using 5% PECC-1CA has shown nrthe best performance, better elastic response compared to 2% coupling agent, which is consistent to the J analysis. Samples better elastic response compared to 2% coupling agent, which is consistent to the Jnr analysis. Samples tested using lower stress levels have resulted in smaller non‐recoverable compliance and superior in in terms of non-recoverable compliance criteria and percent recovery after continuously multiple tested using lower stress levels have resulted in smaller non‐recoverable compliance and superior in terms of percent recovery. This is clearly simulated the condition in the field, where heavy vehicles loading action on the sample. Referring to the specimens prepared using 3% PECC-1CA and 3% terms of percent recovery. This is clearly simulated the condition in the field, where heavy vehicles (e.g., lorries and trucks) cause more severe permanent deformation compared to other vehicles, as PECC-2CA, application of 1% coupling agent in the PECC material represents better elastic response (e.g., lorries and trucks) cause more severe permanent deformation compared to other vehicles, as we can see the rut depths in the slow lane are typically more severe than the fast lane of a highway. compared to 2% coupling agent, which is consistent to the Jnr analysis. Samples tested using lower we can see the rut depths in the slow lane are typically more severe than the fast lane of a highway. Overall, without the presence of coupling agent, asphalt binder modified using 3% PECC has Overall, without the presence of coupling agent, asphalt binder modified using 3% PECC has stress levels have resulted in smaller non-recoverable compliance and superior in terms of percent shown a better recovery percentage compared to 5% PECC sample. With the addition of coupling shown a better recovery percentage compared to 5% PECC sample. With the addition of coupling recovery. This is clearly simulated the condition in the field, where heavy vehicles (e.g., lorries and agent, a higher percentage could be adopted in the modification process of asphalt binder. However, agent, a higher percentage could be adopted in the modification process of asphalt binder. However, trucks) cause more severe permanent deformation compared to other vehicles, as we can see the rut the amount of coupling agent should be limited to 1% to avoid adverse effects on its resistance to the amount of coupling agent should be limited to 1% to avoid adverse effects on its resistance to depthsrutting. in the slow lane are typically more severe than the fast lane of a highway.
Non-recoverable Non-recoverableCompliance, Compliance, JnrJnr(1/kPa) (1/kPa)
rutting.
33 2.5 2.5
0.1 kPa kPa 0.1 3.2 kPa 3.2 kPa
22 1.5 1.5 11 0.5 0.5 00
Percent PercentRecovery, Recovery,R(%) R(%)
Figure 8. Non‐recoverable compliance for evaluation of rutting potential. Figure 8. Non-recoverable compliance for evaluation of rutting potential. Figure 8. Non‐recoverable compliance for evaluation of rutting potential.
25 25 20 20 15 15 10 10
0.1 kPa kPa 0.1 3.2 kPa 3.2 kPa
55 00
Figure 9. Recovery percentage of the tested asphalt binders. Figure 9. Recovery percentage of the tested asphalt binders. Figure 9. Recovery percentage of the tested asphalt binders.
3.4. Low Temperature Cracking Using BBR Test 3.4. Low Temperature Cracking Using BBR Test The BBR test was conducted to evaluate the low temperature stiffness and relaxation properties The BBR test was conducted to evaluate the low temperature stiffness and relaxation properties of asphalt binders, based on the function of load and duration. These parameters give an indication of asphalt binders, based on the function of load and duration. These parameters give an indication of an asphalt binder’s ability to resist low temperature cracking. of an asphalt binder’s ability to resist low temperature cracking. The data was then analyzed to calculate the critical cracking temperatures (Tcr) of the asphalt The data was then analyzed to calculate the critical cracking temperatures (Tcr) of the asphalt binders based on the measured creep stiffness and m‐values. Figure 10 shows the limiting low binders based on the measured creep stiffness and m‐values. Figure 10 shows the limiting low
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Overall, without the presence of coupling agent, asphalt binder modified using 3% PECC has shown a better recovery percentage compared to 5% PECC sample. With the addition of coupling agent, a higher percentage could be adopted in the modification process of asphalt binder. However, the amount of coupling agent should be limited to 1% to avoid adverse effects on its resistance to rutting. 3.4. Low Temperature Cracking Using BBR Test
5%PECC-2CA
3%PECC-2CA
5%PECC-1CA
3%PECC-1CA
5% PECC
3% PECC
-25
PG58-28
Critical Cracking Temperature (oC)
The BBR test was conducted to evaluate the low temperature stiffness and relaxation properties of asphalt binders, based on the function of load and duration. These parameters give an indication of an asphalt binder’s ability to resist low temperature cracking. The data was then analyzed to calculate the critical cracking temperatures (Tcr ) of the asphalt Appl. Sci. 2018, 8, x FOR PEER REVIEW 10 of 15 binders based on the measured creep stiffness and m-values. Figure 10 shows the limiting low temperature or Tcrcr for each binder. Overall, all the modified asphalt binders have shown comparable for each binder. Overall, all the modified asphalt binders have shown comparable temperature or T performance in terms of resistance to low temperature cracking. It was found that incorporating performance in terms of resistance to low temperature cracking. It was found that incorporating 3% 3% PECC-1CA modifier had contributed thelow lowtemperature temperatureperformance performanceof of the the asphalt PECC‐1CA modifier had contributed to to the asphalt binder, binder, ◦ C, compared to the control asphalt binder that where it could resist the thermal cracking at − 33.2 where it could resist the thermal cracking at −33.2 °C, compared to the control asphalt binder that may only resist the thermal cracking at temperature as low as −30.5 ◦ C. may only resist the thermal cracking at temperature as low as −30.5 °C.
-27 -29 -31 -33 -35
Figure 10. 10. Critical cracking temperature of PECC‐based binders compared to control Figure Critical cracking temperature of PECC-based asphaltasphalt binders compared to control specimen. specimen.
4. Performance of Asphalt Mixtures 4. Performance of Asphalt Mixtures 4.1. Resistance to Permanent Deformation 4.1. Resistance to Permanent Deformation Flow number test was conducted to evaluate the rutting resistance of asphalt pavement. The test Flow number test was conducted to evaluate the rutting resistance of asphalt pavement. The test was typically used to assess the resistance to permanent deformation for the past several years [49,50]. was typically used to assess the resistance to permanent deformation for the past several years [49,50]. Faheem et al. [51] mentioned that flow number test has a strong correlation to the Traffic Force Index Faheem et al. [51] mentioned that flow number test has a strong correlation to the Traffic Force Index (TFI), which represents the densification loading by the traffic during its service life. It was also found (TFI), which represents the densification loading by the traffic during its service life. It was also found that this test has a good correlation with the field rutting performance [52,53]. The test is performed that this test has a good correlation with the field rutting performance [52,53]. The test is performed by introducing repeated traffic loading (loading and unloading) on the cylindrical asphalt specimen by introducing repeated traffic loading (loading and unloading) on the cylindrical asphalt specimen and the permanent deformation is recorded as a function of load cycles at the minimum permanent and the permanent deformation is recorded as a function of load cycles at the minimum permanent strain rate. strain rate. Figure 11 shows the flow number test result. The specimens prepared using modified asphalt Figure 11 shows the flow number test result. The specimens prepared using modified asphalt binders have significantly higher resistance to rutting compared to the control sample. Greater amount binders have significantly higher resistance to rutting compared to the control sample. Greater amount of modifier has resulted in a higher flow number, which indicated a better resistance to rutting. The addition of coupling agent also has remarkably increased the mixture stiffness that contributes to lower rutting potential.
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of modifier has resulted in a higher flow number, which indicated a better resistance to rutting. The addition of coupling agent also has remarkably increased the mixture stiffness that contributes to 11 of 15 lowerAppl. Sci. 2018, 8, x FOR PEER REVIEW rutting potential.
Flow Number (Cycle) Flow Number (Cycle)
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350 350 300 300 250 250 200 200 150 150 100 100 50 50 0 0
Sample Sample Figure 11. Flow number test results. Figure 11. Flow number test results.
Figure 11. Flow number test results.
4.2. Moisture Susceptibility 4.2. Moisture Susceptibility
Indirect Tensile Strength, ITSITS Indirect Tensile Strength, (kPa) (kPa)
4.2. Moisture Susceptibility Figure 12 shows the ITS values of tested samples. Overall, the addition of modifiers does not Figure 12 shows the ITS values of tested samples. Overall, the addition of modifiers does not significantly alter the ITS of the sample in the dry condition, except 5% PECC‐2CA. There are no Figure 12 shows the ITS values of tested samples. Overall, the addition of modifiers does not significantly alter thethe ITSITS ofof the sample in dryof modifiers and condition,except except PECC-2CA. are no significant effects of using different compositions the coupling agent in There terms of significantly alter the sample in the the dry condition, 5% 5% PECC‐2CA. There are no significant effects of using different compositions of modifiers and the coupling agent in terms indirect tensile strength results as indicated by the error bars presented. However, the modifiers help significant effects of using different compositions of modifiers and the coupling agent in terms of of indirect tensile strength results as indicated by the error bars presented. However, the modifiers help in enhancing the ITS values of the wet samples. The samples incorporated lower amount of modifiers indirect tensile strength results as indicated by the error bars presented. However, the modifiers help (3%) have a better ITS value compared to sample prepared using 5% modifiers. Incorporating 1% and in enhancing the ITS values of the wet samples. The samples incorporated lower amount of modifiers in enhancing the ITS values of the wet samples. The samples incorporated lower amount of modifiers 2% coupling agents also do not have significant differences between them in term of wet samples’ (3%) (3%) have a better ITS value compared to sample prepared using 5% modifiers. Incorporating 1% and have a better ITS value compared to sample prepared using 5% modifiers. Incorporating 1% and ITS values. 2% coupling agents also do not have significant differences between them in term of wet samples’ 2% coupling agents also do not have significant differences between them in term of wet samples’ ITS values. ITS values.
1400 1400 1200 1200 1000 1000 800 800 600
Dry Dry Wet Wet
600 400 400 200 2000 0
Figure 12. ITS test results.
Figure 12. ITS test results. Figure 12. ITS test results. Based on Figure 13, additions of modifiers have remarkably improved the TSR of modified asphalt mixtures compared to the control mixture, except specimen incorporating 5% of PECC‐2CA. Based on Figure 13, additions of modifiers have remarkably improved the TSR modified Combination of 3% PECC and coupling agent at 1% and 2% has greatly enhanced the resistance to asphalt mixtures compared to the control mixture, except specimen incorporating 5% PECC‐2CA. Combination of 3% PECC and coupling agent at 1% and 2% has greatly enhanced the resistance to
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Based on Figure 13, additions of modifiers have remarkably improved the TSR of modified asphalt Appl. Sci. 2018, 8, x FOR PEER REVIEW 12 of 15 mixtures compared to the control mixture, except specimen incorporating 5% PECC-2CA. Combination
Tensile Strength Ratio, TSR
of 3% PECC and coupling agent at 1% and 2% has greatly enhanced the resistance to moisture damage moisture damage of asphalt mixture. However, the combination of the coupling agent with 3% PECC of asphalt mixture. However, the combination of the coupling agent with 3% PECC is optimum for is optimum for this study in order to avoid adverse due to moisture damage. The combination of 5% this study in order to avoid adverse due to moisture damage. The combination of 5% PECC and 2% PECC and 2% coupling agent yield mixtures with worse moisture susceptibility characteristic as coupling agent yield mixtures with worse moisture susceptibility characteristic as compared to other compared to other modified mixtures. modified mixtures.
1.2 1 0.8 0.6 0.4 0.2 0
Figure 13. Moisture susceptibility of asphalt mixtures. Figure 13. Moisture susceptibility of asphalt mixtures.
5. Conclusions 5. Conclusions Based on the outcome of this study, several conclusions can be made as follows: Based on the outcome of this study, several conclusions can be made as follows:
1. 1. 2. 2.
3. 3.
4. 4. 5. 5.
6. 6.
Addition of LLDPE‐CaCO Addition of LLDPE-CaCO3 modifiers and coupling agent do not significantly affect the volatile 3 modifiers and coupling agent do not significantly affect the volatile loss of modified asphalt binders. loss of modified asphalt binders. Modified asphalt binders have higher viscosity value compared to the control asphalt binder. Modified asphalt binders have higher viscosity value compared to the control asphalt binder. The addition of a titanate‐coupling agent has slightly increased the viscosity and consistency of The addition of a titanate-coupling agent has slightly increased the viscosity and consistency asphalt binders depending on the of coupling agent agent and test The of asphalt binders depending on percentage the percentage of coupling and temperature. test temperature. viscosity of asphalt binder could also be used as an early indicator of resistance to permanent The viscosity of asphalt binder could also be used as an early indicator of resistance to permanent deformation. deformation.The Theaddition additionof ofmodifiers modifiersand andcoupling couplingagent agent has has significantly significantly improved improved the the resistance to permanent deformation of asphalt binders. resistance to permanent deformation of asphalt binders. With the addition of coupling agent, a higher percentage could be adopted in the modification With the addition of coupling agent, a higher percentage could be adopted in the modification process of asphalt binder. However, the amount of coupling agent should be limit to 1% to avoid process of asphalt binder. However, the amount of coupling agent should be limit to 1% to avoid adverse effects on its resistance to rutting. adverse effects on its resistance to rutting. Overall, Overall,all all the the modified modified asphalt asphalt binders binders have have shown shown comparable comparable performance performance in in terms terms of of resistance to low temperature cracking. resistance to low temperature cracking. A greater amount of modifier has resulted in a higher flow number, which indicated a better A greater amount of modifier has resulted in a higher flow number, which indicated a better resistance to rutting. The addition of coupling agent also has remarkably increased the mixture resistance to rutting. The addition of coupling agent also has remarkably increased the mixture stiffness that contributes to lower rutting potential. stiffness that contributes to lower rutting potential. The modifiers help in enhancing the ITS values of the wet samples. The combination of the The modifiers help in enhancing the ITS values of the wet samples. The combination of the coupling agent with 3% PECC is optimum for this study to avoid adverse due to moisture coupling agent with 3% PECC is optimum for this study to avoid adverse due to moisture damage. damage.
Author Contributions: Rosli Mohd Hasan (Data(Data curation, Writingoriginaloriginal draft, Methodology) Zhanping Author Contributions: Mohd Mohd Rosli Mohd Hasan curation, Writing‐ draft, Methodology) You (Supervision, Project administration, Writing- review & editing), Mohd Khairul Idham Mohd Satar (Formal Zhanping You (Supervision, Project administration, Writing‐ review & editing), Mohd Khairul Idham Mohd analysis, Writing- review & editing), Muhammad Naqiuddin Mohd Warid (Formal analysis, Writing- review & Satar (Formal analysis, Writing‐ review & editing), Muhammad Naqiuddin Mohd Warid (Formal analysis, Writing‐ review & editing), Nurul Hidayah Mohd Kamaruddin (Formal analysis, Writing‐ review & editing), Dongdong Ge (Formal analysis, Writing‐ review & editing), Ran Zhang (Formal analysis, Writing‐ review & editing)
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editing), Nurul Hidayah Mohd Kamaruddin (Formal analysis, Writing- review & editing), Dongdong Ge (Formal analysis, Writing- review & editing), Ran Zhang (Formal analysis, Writing- review & editing). Acknowledgments: The authors grateful to express their appreciation to Kenrich Petrochemicals, Inc. (Bayonne, NJ, USA), Specialty Minerals Inc. (Bethlehem, PA, USA), Payne & Dolan Inc. (Waukesha, WI, USA), and Dow Chemical Company (Midland, MI, USA) for donating test materials. The authors would like to acknowledge the research assistantships to Mohd Rosli Mohd Hasan, Mohd Khairul Idham Mohd Satar, Muhammad Naqiuddin Mohd Warid, Nurul Hidayah Mohd Kamaruddin, Ran Zhang, and Dongdong Ge. The authors also want to acknowledge Julia A. King from Department of Chemical Engineering of Michigan Technological University for her significant contributions in materials preparation, test design, and paper revision. It is impossible for the authors to complete the work without her effort. Any opinions, findings and conclusions expressed in this paper are those of the authors’ and do not necessarily reflect the views of the official views and policies of any institution or company. Conflicts of Interest: The authors declare no conflict of interest.
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